In the production of minerals, e.g., oil and gas, certain properties of a subterranean reservoir must be determined. One of the most important of these properties is the permeability of the reservoir. Permeability of a material is a measure of the ability of the material to transmit fluids through its pore spaces and is inversely proportional to the flow resistance offered by the material. Normally, permeability is determined by taking core samples from the reservoir and carrying out well-defined measurement techniques on the samples. There are several techniques available for making such measurements, many of which are described in PETROLEUM PRODUCTION ENGINEERING--DEVELOPMENT by L. C. Uren, Fourth Edition, McGraw-Hill Book Company, Inc., 1956, pps. 660-669. Another standard reference is American Petroleum Institute, API RECOMMENDED PRACTICE FOR CORE-ANALYSIS PROCEDURE, API RP40, 1960.
More particularly, the relative permeability plays a very important role in describing the fluid flow in oil and gas reservoirs. Two methods of measurement are practiced by the industry, steady-state and dynamic displacement. In each method a cylindrical core is saturated with water or brine, then oil flooded to irreducible water saturation. Subsequently the core is waterflooded or brine flooded and the pressure drop across the core is measured along with the oil and water or brine production. The average saturations within the core are determined from the overall material balance. The steady-state method requires lengthy measurement times because it requires stabilization of the fluid flow. The dynamic displacement method overcomes this, however, it suffers from capillary and effects. Hence the displacement method is only effective for high flow rates.
It is therefore an object of the present invention to provide a new and improved method for determining the relative permeability of a subterranean reservoir by way of selective measurements on a core sample from such reservoir.